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【单选题】
放大电路如图11-11所示，设晶体管β=50，RC=1．5kΩ，Ube=0．6V，为使电路在可变电阻R=0时，晶体管刚好进入饱和状态，电阻R应取（）kΩ。A.
72
B.
100
C.
25
D.
50
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【单选题】Which of the following statements is correct about propagation rules?
A.
In the MF/HF band, Iow frequency is selected for long distance communication.
B.
The frequency selected during nighttime is lower than that selected during the daytime if the receiver is the same one.
C.
In the MF/HF band, the frequency selection bas nothing to do with the communication distance.
D.
The frequency selected during daytime is lower than that selected during the night time if the receiver is the same one.
【简答题】有下列叙述： ①集合 {x∈N|x= 6 a ，a∈N * } 中只有四个元素； ②设a＞0，将 a 2 a? 3 a 2 表示成分数指数幂，其结果是 a 5 6 ； ③已知函数 f(x)= 1+ x 2 1- x 2 (x≠±1) ，则 f(2)+f(3)+f(4)+f( 1 2 )+f( 1 3 )+f( 1 4 )=3 ④设集合 A=[0， 1 2 ， B=[ 1 2 ，1] ，函数 f(x...
【单选题】以下4个集合中有几个是线性空间() 1)设A是n阶方阵,A的实系数多项式全体对于矩阵的加法和数乘运算; 2)全体实对称矩阵对于矩阵的加法和数乘运算; 3)平面中不平行于某一向量的全体向量所成集合对于向量加法和数乘运算; 4)闭区间[a,b]上全体可导函数全体关于函数的加法和实数域函数的乘法。
A.
0
B.
1
C.
2
D.
3
【单选题】听力原文： Botany, the study of plants, occupies a peculiar position in the history of human knowledge. For many thousands of years it was the one field of awareness about which humans bad anything more th...
A.
Botany is a very ancient learning.
B.
People in the Stone Age knew a lot about plants.
C.
People in the Stone Age knew little about plants.
D.
Pre-industrial societies have little insights about plants.
【简答题】表征聚合物相对分子质量的参数有 和
【单选题】听力原文： Botany, the study of plants, occupies a peculiar position in the history of human knowledge. For many thousands of years it was the one field of awareness about which humans had anything more th...
A.
Botany is a very ancient learning.
B.
People in the Stone Age knew a lot about plants.
C.
People in the Stone Age knew little about plants.
D.
Pre-industrial societies have little insights about plants.
【单选题】Section A Directions: In this section, you will hear 8 short conversations and 2 long conversations. At the end of each conversation, one or more questions will be asked about what was said. Both the ...
A.
Swimming.
B.
Playing basketball.
C.
Boating.
D.
Playing volleyball.
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